1. Field of the Invention
The present invention relates to zoom lenses, and more particularly, to a zoom lens suitable for use as an imaging lens in an image pickup apparatus, such as a digital still camera, a video camera, a monitoring camera, a broadcast camera, or a film camera.
2. Description of the Related Art
A zoom lens having a small overall lens length (distance from a first lens surface to an image plane) and a high zoom ratio is required as an imaging lens for use in an image pickup apparatus including a solid-state image pickup device, such as a CCD or a CMOS.
A positive lead type zoom lens is known which includes, in order from the object side to the image side, a first lens unit having a positive refractive power (optical power is the reciprocal of a focal length), a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a rear lens group including one or more lens units.
U.S. Pat. No. 7,830,613 discloses a zoom lens which includes, in order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power and in which all of the lens units are moved during zooming.
U.S. Pat. No. 7,593,164 discloses a zoom lens which includes, in order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a negative refractive power, and a fifth lens unit having a positive refractive power.
In general, the size of a zoom lens can be reduced while maintaining a certain zoom ratio by increasing the refractive power of each of the lens units included in the zoom lens and reducing the number of lenses. However, in such a zoom lens, aberrations largely vary during zooming and it is difficult to obtain high optical performance over the entire zoom range. In particular, large aberrations, such as chromatic aberration, which are difficult to correct are generated at the telephoto end.
The present invention provides a small high-zoom-ratio zoom lens having high optical performance over the entire zoom range and an image pickup apparatus including the zoom lens.